Phytoplankton distributions

Question 1

Growth and loss

Answer 1

Growth controlled by bottom up factors:
- availability of key resources such as light and nutrients
Loss is equally important in dictating overall biomass and net growth of populations.
Loss controlled by top down, grazing, sinking, viral infection

Question 2

Models

Answer 2

dP/dt = P (u - (g + M))
dP/dt > rate of change of phyto (P)
Growth rate (u) a function of bottom up factors
Loss rate through grazing (g) and other mortality (m)

Question 3

Seasonal succession

Answer 3

Different groups of phytoplankton may dominate as environmental conditions vary through the season
Diatoms –> green algae –> blue greens –> diatoms

Question 4

Margalef’s Mandela

Answer 4

High nutrient, high turbulence:
- diatoms, large cells, high max growth rates, grazer defence.
LN,LT:
- Prochlorococcus, effective competition for resources, small cells (low Kn), reduction of cellular nutrient requirements.
HN,LT
- red tide dinos, motility (retention in the bloom), toxic (grazer and competitor deterrence/inhibition)

Question 5

Time series stations

Answer 5

Bermuda Atlantic Time Series (BATS)
Hawaii Ocean Timeseries (HOT)

Question 6

Succession at BATS

Answer 6

North Atlantic sub tropical gyre
Seasonal cycle, winter bloom when mixed layer penetrates nitracline followed by oligotrophic summer stratified period
Seasonal succession:
Eukaryotes during bloom –> prokaryotes

Question 7

Succession at HOT

Answer 7

Highly stratified oligotrophic system
No strong spring or winter bloom
Low nutrients in surface throughout the year

Question 8

Stratified low nutrient systems

Answer 8

Inputs of new nutrients through mixing are low, production dominated by regeneration N
F-ratio is low all year
Some prochlorococcus ecotypes have lost the ability to grow on new N sources as it is so low
Different ecotypes have become adapted to different degrees of oligotrophy through gene loss

Question 9

Deep Chlorophyll maximum

Answer 9

In stratified oligotrophic systems a sub-surface DCM forms
The DCM is v common and found at base of the surface mixed layer and top of the nutricline
DCM can have a different community structure compared to the surface due to difference in light and nutrient availability

Question 10

Seasonal cycle in a shelf sea

Answer 10

Both the seasonal cycle and the presence of the DCM reflect the availability of light and nutrients
Not all regions of a shelf sea stratify in summer

Question 11

Fronts in shelf seas

Answer 11

Surface water temperatures indicate boundaries between mixed waters and stratified waters

Question 12

Compare seasonal cycle and front

Answer 12

• Mixed water:
• High nutrients, low light, light limiting growth.
• Highly stratified:
• Low nutrients, high light, nutrient limiting.

Question 13

Cyclonic Eddys

Answer 13

Anticlockwise in N hemi
Ekman deflection leads to surface water moving away from centre of eddy.
Upwelling can bring nutrients upwards towards the nutrient limited layers
Can enhance:
PP, new production.
Phyto growth in DCM often dominated by diatoms

Question 14

Anticyclonic eddy

Answer 14

Clockwise in N hemi
Ekman deflection leads to surface water moving towards centre of eddy.
Downwelling